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 Post subject: Converting AC to DC at the house level.
PostPosted: Mon Jun 21, 2010 12:45 am 
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I had a weird thought a few days ago and tried to search on google. All I got was acdc music or washington dc links for my trouble.

My thought had to do with the antec cp-850. It is able to give efficient, quite, and cool ac to dc power conversion, using cheap parts because it's put in a much bigger box.

Why can this not be done on the house level instead of device by device. We could have a big box that does ac to dc conversion like we got air conditioners and water heaters.

Have AC come into the house and into the box and then out as DC to the rest of the house. I would think at this level for a few thousand dollars, you could get better then 90% effectiveness pretty easily.

Wonder how much power worldwide we could save by doing this. When you got devices that have sub 50% effectiveness. Let alone not needing to put ac to dc converters into every single electronic device sold.

Any thoughts on this.


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 Post subject: Re: Converting AC to DC at the house level.
PostPosted: Mon Jun 21, 2010 2:15 am 
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You said it :P

Freyr wrote:
for a few thousand dollars, you could get better then 90% effectiveness pretty easily.


Most people could buy CP-850's for all the computers in their house for that money, and other appliances often don't go well with 12v.

You tv? Needs more than 12 volt. Hi-Fi system? More than 12 volt. The same goes for your dishwasher, monitor, etc etc. The only appliance that would benefit would be the desktop PC, the current would become too high for other equipment.


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 Post subject: Re: Converting AC to DC at the house level.
PostPosted: Mon Jun 21, 2010 3:14 am 
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Freyr wrote:
Have AC come into the house and into the box and then out as DC to the rest of the house. I would think at this level for a few thousand dollars, you could get better then 90% effectiveness pretty easily.
Sure, if we're talking high voltage DC. But then we need to re-build all appliances to accept DC instead of AC...

If you want low voltage DC distributed you'll need much thicker cables to handle all current without losing voltage and power between the transformer and appliance.

In the end it's all too expensive.

Cheers
Olle


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 Post subject:
PostPosted: Mon Jun 21, 2010 3:49 am 
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If you would keep the old cables, then resistance stays the same. Now if you go down to 12V from 120V, this happens:

- To be able to deliver equal power, you need 10x the current when using 1/10th of the voltage.
- The power loss is current to the second power times the resistance. This gives 100x times the power loss in the cables!
- To get the power loss back to the original levels, either the cables need to be 1/100 of their original length, or their cross sectional area needs to be 100x higher, which in turn means that they need to be 10x as thick.

To summarize, it's not feasible.

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 Post subject:
PostPosted: Thu Jul 01, 2010 10:42 am 
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This is an interesting idea... you could look at it from the other side though: instead of converting 120VAC to 12VDC, why not keep it closer to 120VDC? That way you wouldn't have to reduce the current to get the same amount of power. The only downside is, you'd have to use hefty components to be able to handle the current... IIRC, any electrical component rated for X amps using AC power will only handle 1/2X amps on DC. I believe it's because the amperage in AC is determined by the difference between the two amplitudes (positive and negative), whereas in DC it's calculated by the difference between the amplitude (positive) and 0. But, I'm not an electrical engineer, so I don't know for certain.

In any event, you'll never reach exceptionally high efficiencies for the cost, at least not when you compare it the efficiency of some PSUs on the market. You might be better off converting to something like 12VDC in the walls or with a standalone transformer, and running it to your PC using heavy gauge automotive wiring. I think a 4 gauge cable would handle up to about 150 amps. However, you'd still have to find some way to get the lower voltages required inside the computer, which requires more transformers. Then, assuming you have an in-wall unit, you'd be limited to where you can locate your components (unless you wire your entire house with both AC and DC, with outlets for both).

However, still an interesting idea, and it may be possible to modify an existing PSU with longer cables and mounting it away from the rest of the computer... thus, you can use any PSU you want, locate it anywhere, and reduce the heat inside the case.

As an aside, I think a lot of amplifiers actually use 12VDC in their internals... I think the only real difference between them and a PC is that they use a single voltage and can get away with one large transformer, rather than several smaller ones. Amplifier transformers also aren't designed to be swapped from one unit to another, so they don't have to fit a particular form factor or be nicely packaged.

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 Post subject:
PostPosted: Thu Jul 01, 2010 12:16 pm 
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pope_face wrote:
...The only downside is...


What on earth is the upside of what you propose? I can't see anything positive in it.

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 Post subject:
PostPosted: Thu Jul 01, 2010 4:17 pm 
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lm wrote:
pope_face wrote:
...The only downside is...


What on earth is the upside of what you propose? I can't see anything positive in it.


Ah, my mistake... I suppose it's more a figure of speech than pros and cons. You had previously mentioned that to get the same amount of power from a 12V system, the cables would need a cross-section 100x that of a 120V system in order to handle the current. I was simply suggesting an alternative, that instead of converting to 12VDC, it could be converted to 120VDC. It seems to me that 120VDC could provide the same power as 120VAC at the same current... thus, no need for extremely heavy gauge wires.

Again, I don't know that much about electronics, so I can't say for certain what is or isn't true, and I wasn't suggesting this to be the greatest idea of the 21st century. I'm simply looking at this as an exercise in thought, that's all.

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 Post subject:
PostPosted: Thu Jul 01, 2010 10:17 pm 
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You might find it interesting to read some about the history of electricity distribution,
e.g. the competition between DC and AC transmission
(Edisson vs. Westinghouse & Tesla)
http://en.wikipedia.org/wiki/War_of_Currents

(Used to use DC - but AC won out because, with the technology then available, it was easier to convert voltages.)

Also, there are lots of sites about going "off grid" - using
solar panels and batteries (which work in DC) to power homes.
They might have useful perspectives on the merits of DC vs AC
in the home.

The idea that has been mooted a few times here of using one AC-DC power supply for an entire computer system makes a lot of sense.
Have connectors to power the monitor, speakers, scanner, external drives, etc. from the AC-DC converter that powers the computer. (Share one power converter, would be easily adapted to use a battery as a UPS - without having loss of going from AC to DC to AC to DC.)


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 Post subject:
PostPosted: Sat Jul 03, 2010 10:58 am 
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SCDR: That was an interesting read... thanks for the suggestion. It answered my thoughts about converting from 120VDC to 12VDC... I didn't realize it was so complex. I'm trying to find ways to convert the voltage in my car from 12VDC to lower voltages (to run certain components), but the "converters" (I don't know the actual word) are hard to find. Now I know why.

I forgot about "off-grid" power, but I remember reading about it a few times. Same deal with cars, motorbikes, electric wheelchairs, power scooters, and all those electrical components you mentioned (plus many more that will work, or can be converted). As an aside: I've got a few old PSUs kickin' around in my house from various PC builds, and I've used the 12VDC output to test automotive headunits and such. I'm also curious what kind of power gasoline/diesel generators put out: Whether it's straight AC with the voltage stepped up/down, or DC that's then converted to AC.

As a final note: It says at the end of the article that DC power was used in some buildings until 2007, at which point everything switched over to AC (although transformers were provided for some people who still use DC within their house). I found it interesting that the subject of this thread was actually relatively common for some 50 years, and persisted until 3 years ago.

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 Post subject:
PostPosted: Sun Jul 04, 2010 1:19 am 
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Actually now (as compared to in Edison's day) it is reasonably easy to convert DC to DC. There are DC to DC power supplies (like the PicoPSU for computers), and various circuits/ICs/etc. that do the job.

(e.g., Look up DC to DC converter, http://en.wikipedia.org/wiki/DC_to_DC_converter or Charge Pump.)

Of course in a car you also have to deal with the vagaries of the electrical system (the nominal 12V can vary quite a bit, depending on whether the car is being started, being run, engine is off and running device off batteries).

There are lots of DC to DC converters for use in cars. (Websites and books about car computers might give you some leads on power supplies, even if what you are working on isn't car related.)


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 Post subject:
PostPosted: Sun Jul 04, 2010 10:09 am 
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scdr wrote:
Actually now (as compared to in Edison's day) it is reasonably easy to convert DC to DC. There are DC to DC power supplies (like the PicoPSU for computers), and various circuits/ICs/etc. that do the job.


Haha, maybe I just haven't looked hard enough. I hadn't thought about the PicoPSU, but that has to be the best idea yet. I only really need a few amps on 5V as well as the standard 12V, so it's perfect (and cheap). As for power variance: perhaps some sort of voltage regulator/capacitor? I won't be running any components that are sensitive to a loss of power, so that's not as much of a concern as the extra 1.4V under normal operating conditions.

But, this is not an automotive forum, so I apologize for the off-topic discussion.

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 Post subject:
PostPosted: Sun Jul 04, 2010 9:55 pm 
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If you use PicoPSU for automotive - probably want the one that has a voltage regulator so can take wider input range (the basic ones just pass the 12v through). There are various other supplies for Car PCs (although a lot of them get fancy dealing with startup signals, etc.)


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 Post subject:
PostPosted: Tue Jul 13, 2010 8:58 am 
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If you were thinking about having DC around your house, that can easily be arranged if you got a couple of spare PSU's (hehe)...

Why not just rip out a plug from your wall, take the AC wires and solder them to the power connector.

Split the power wires and connect it to the plug, minding polarity.
12V on the top one, 5V on the bottom one.

Wrap it up, trim some extension cords and run it to your computer.

The only problem with this is that you may have to fit the whole thing inside your wall, which can be done if you dont mind cutting a hole in your wall (and adding a vent possibly instead of drywall).



-Having DC around your house would be very inefficient. The wire that runs all over your house has resistance in it, which will cause losses, so 12V at the PSU would be 7V on the other side of the house.


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 Post subject:
PostPosted: Fri Jul 16, 2010 11:25 am 
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I work in the telecom industry. What you are suggesting is essentially how you build Telco Central Offices (COs) and Mobile Telephone Switching Offices (MTSOs). Power comes in from the grid and is converted to 48vdc in very large (10,000 amp or more) rectifier plants and then filtered/stored in large lead-acid battery arrays. It is a 95%+ efficient conversion. It makes the local power supplies in the equipment much simpler. This is also why your phones still work during a regional power outage...

One problem is that this requires MASSIVE copper plant to distribute the power. In most of the larger, more efficient offices this means copper bussbar distribution - think of power distributed over a buss made up of 1/2 inch thick by 6 in wide copper plates stacked up to 8 inches thick (with voids to allow expansion & cooling). And then you distribute from the buss using distribution cables that start at 6-0 copper and get as large as 750MCM (think of 2.5 inch thick stranded copper cable). It is pretty damn expensive stuff.

You also have DC power running at current levels that are actually dangerous. 50-100amp individual circuits are common, higher ones are not unusual. In a home situation with 12v distribution you would have a similar problem with high current / large copper / dangerous current.

Overall - its probably not a good idea...whatever you might save from a few watts conversion efficiency will be lost to higher copper demand worldwide and a few lost lives from shock hazards that would have been harmless at 110v/15A.


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 Post subject:
PostPosted: Mon Jul 19, 2010 6:04 pm 
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piglover wrote:
This is also why your phones still work during a regional power outage...


This I never knew... I've often wondered about it, so thanks for the tidbit.

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 Post subject: Re: Converting AC to DC at the house level.
PostPosted: Wed Jan 26, 2011 10:14 pm 
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If you go off the grid you are creating your own electricity, and usually the electricity you are creating is dc rather than the ac we get from the power company. For use in the home many people who make their own electricity are using an inverter or generator to convert this to ac; my question is why? I'm looking at the things I have plugged into various recepticals around the house, and I see a bunch of devices that have the black boxes between the device and the receptical; these convert ac to dc. There are also many devices that take the ac and convert it to dc internally before anything else is done; most things like dc much more than ac.
It's true dc is more dangerous than ac, just as driving is more dangerous than public transportation and stupid is more dangerous than smart. I think it is possible to create a system to handle dc without exposing the user to danger; of course there will always be someone who will try to defeat any safeguard put into place; I've already talked about stupid/smart. I haven't checked into laws and liabilities, but I'd believe government would have something to say on the matter as well.
Going from dc to ac and back to dc creates a significant loss and isn't necessary for many of the devices in the home. When your electricity is created miles away, it may be better to send it to you in the form of ac, but if you are making it on your roof or in your back yard, perhaps we should get used to the idea of living in dc based homes.


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 Post subject: Re: Converting AC to DC at the house level.
PostPosted: Wed Apr 13, 2011 9:28 am 
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those little black boxes each one has a different output voltage and some just drop voltage down but stay AC.


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 Post subject: Re: Converting AC to DC at the house level.
PostPosted: Fri Jul 08, 2011 5:18 am 
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This maybe a holy thread revail but just to say i have worked on something like this.

It is immentiagley possible in the home. PC power supply would not work so well, maybe a few of them. I am actually very tempted to use one of the PSU we looked at to make a silent PC. Its a 94% Ac to DC conversion, fanless PSU. Use this as a power brick then plug in to car PC convertor? Anyone think it is feasible?
http://www.meanwelldirect.co.uk/product ... efault.htm

On topic in terms of house wiring the advantages of doing this are
• Better for new micro/grid sources. In particular if you are doing battery storage for grid shifting or integrating with your electric car.
• Most wall warts/ powersupplies are crap. A good central one can be more efficient and cheaper.
• Much safer
• Cheaper devices if adapted to use supply
As others have said the amount of power you can distribute is a problem because your losses are proportional to voltage squared. The telecoms solution of 48 volts is hence 16 times – 4 squared better than using PC solutions.


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